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Old 16-06-2017, 09:02   #31
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Re: Epoxy / Polyester Resins Question

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Check out what MAS has to say about epoxy, vinylester and polyester attributes. I agree with every single thing they say.
I don't disagree with anything they say, but naturally, it is written in such a way to benefit their position.

e.g. "Finished polyester hulls are still suffering from osmotic blistering when untreated by an epoxy barrier coating against water."

Correct, but many polyester hulls show no signs of blistering after 40 years, and should they, they can be coated with an epoxy barrier coat relatively inexpensively.

I do it all the time.

This is far less expensive than building an entire hull out of epoxy vs polyester and just as effective.

The reason they omitted these facts, is that it does not serve their purpose, ie, the communication piece is biased in their favour, to increase their business, which is the entire intent for the piece.
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Old 16-06-2017, 14:01   #32
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Re: Epoxy / Polyester Resins Question

The OP did not specify if they wanted this info for structural or cosmetic work. The type of bond in structural is critical and one needs to follow specific rough up for the mechanical bond. One also needs to know if the underlying resin was blush or non-blush, that is did it contain a wax. I have seen problems with polyester resin separating from the base material, but not having been the installer I dont know if it was bad prep, too thick a layup or the resin kicked too quick.

I prefer expoxy resin because the mix is usually 1;1 or 2:1, and you get a little more working time in hot weather. I also found that 3M Scotch Brite stripping wheels do a great job of roughing up the underlaying base material. I also like to mix chopped glass, cabosil and/or micro balloons to make sure I get a good bond in structural applications.
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Old 16-06-2017, 14:05   #33
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Re: Epoxy / Polyester Resins Question

And NevisDog is on Point!!!

Dont let too much time elapse between layers. As soon as the first layer is tacky, you better start the next. Avoid waiting 24 hours between coats,,,,,,,,,, and NEVER do one layer each weekend.
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Old 16-06-2017, 15:18   #34
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Re: Epoxy / Polyester Resins Question

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I disagree. For over 40 years, manufacturers and pro repair people have been repairing polyester FRP and gelcoat with polyester FRP and gelcoat. Millions and millions of boats.
Agreed, and I think we have all seen and heard of millions of millions of faults, failures and ****-ups with polyester boats...

Perhaps someone will know - do Lloyds or DNV or ABS permit/approve repairs using polyester or do they insist on epoxy? I know my own boat bounced off a reef, with the previous owner. The repair yard in NZ, which carries out hundreds of similar repairs (also many hundreds of osmosis repairs for insurance companies) uses only epoxy in these repairs: anything else and I would not have even considered purchasing her.
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Old 16-06-2017, 15:27   #35
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Re: Epoxy / Polyester Resins Question

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The OP did not specify if they wanted this info for structural or cosmetic work. The type of bond in structural is critical and one needs to follow specific rough up for the mechanical bond. One also needs to know if the underlying resin was blush or non-blush, that is did it contain a wax. I have seen problems with polyester resin separating from the base material, but not having been the installer I dont know if it was bad prep, too thick a layup or the resin kicked too quick.

I prefer expoxy resin because the mix is usually 1;1 or 2:1, and you get a little more working time in hot weather. I also found that 3M Scotch Brite stripping wheels do a great job of roughing up the underlaying base material. I also like to mix chopped glass, cabosil and/or micro balloons to make sure I get a good bond in structural applications.
Coupl notes.

With polyester resin you can set potlife to what you need by altering catalyst ratio. Fillers do not contribute to bond (adhesion), just structural strength and bulk.
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Old 19-06-2017, 11:28   #36
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Re: Epoxy / Polyester Resins Question

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Perhaps someone will know - do Lloyds or DNV or ABS permit/approve repairs using polyester or do they insist on epoxy?
IMHO best industry practice is , (and I have heard some insurance companies insist upon) repairs be made with like materials the vessel was originally constructed of.

ie. Repair polyester with polyester, and epoxy with epoxy.
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Old 19-06-2017, 11:38   #37
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Re: Epoxy / Polyester Resins Question

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IMHO best industry practice is , (and I have heard some insurance companies insist upon) repairs be made with like materials the vessel was originally constructed of.

ie. Repair polyester with polyester, and epoxy with epoxy.
Having handled hundreds of insurance damage claims i believe you are taking this out of context and carrying it further than the underwriters intended. They will routinely defer to the "best practices" as defined by the surveyor they have hired to validate any estimates. Most often these repair estimates will be negotiated between the surveyor and the company providing the estimates.
I have never and will never approve polyester on polyester for structural or below the water line repairs but I have no issue with its use on cosmetic or low stress repairs above the water line.
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Old 19-06-2017, 12:02   #38
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Re: Epoxy / Polyester Resins Question

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Agreed, and I think we have all seen and heard of millions of millions of faults, failures and ****-ups with polyester boats...
I am personally familiar with 100s of boats that were manufactured using polyester resin. Most were well constructed and are still going strong after 20, 30, and 40 years. We celebrated my own polyester resin FRP constructed boats 40th birthday 2 years ago.

It has a few fibreglass issues, mostly due to manufacturer error, DIY modification, or neglect. I suspect it would have at least as many issues, maybe more, if it were made out of epoxy.

Many complaints about polyester I hear, are from those who bought an old boat, really cheap because of lack of proper maintenance, that have issues due to that same lack of proper maintenance, for many, many years.

Typical complaints regarding polyester FRP boats, are related to moisture ingress, osmosis or wood delamination.

Osmosis, (if present, not all boats are subject to it) can be resolved when addressed early in its progression by a simple sanding and epoxy barrier coat application.

It is only when the boat has been neglected and not maintained properly for several years (by applying a barrier coat at first sign of osmosis), that it becomes a major issue.

Wood core delamination usual happens when deck or transom fitting bedding fails, and water is absorbed into the core. When this happens, delamination will result, whether the epoxy or polyester resin was used. This is also a common source of bulkhead tabbing failure. The composite was not properly sealed, and moisture got into the wood, causing the FRP bond to fail. Again this will occur where the resin is FRP or epoxy.

Most bedding materials have a life expectancy of about 10 years. This means that all wood core penetrations should be rebed (parts removed, core checked for wetness, dried or repaired if wet, and new bedding material applied to the joint, not just silicone sealant around the perimeter), every 10 years of the vessel life. If the bedding fails and the core absorbs moisture, and the FRP delaminates, due to complete lack of necessary maintenance, it is not a resin fault.

In years past, the life expectancy of a rec wood boat was about 10 years average, and annual maintenance to achieve that was brutal.

Since the advent of FRP, vessel life expectancy has increased substantially, probably to about 25 years average, and that number is likely about the same for polyester or epoxy, everything else being equal.

Of course there will be extremes at either end of the bell curve.
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Old 19-06-2017, 12:03   #39
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Re: Epoxy / Polyester Resins Question

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Agreed, and I think we have all seen and heard of millions of millions of faults, failures and ****-ups with polyester boats...

Perhaps someone will know - do Lloyds or DNV or ABS permit/approve repairs using polyester or do they insist on epoxy? I know my own boat bounced off a reef, with the previous owner. The repair yard in NZ, which carries out hundreds of similar repairs (also many hundreds of osmosis repairs for insurance companies) uses only epoxy in these repairs: anything else and I would not have even considered purchasing her.
No standards organization will ever specify a specific product (resin) be used in any circumstance. What they do is lay out the requirements that product must meet.

ABS and the USCG requires that the adhesive properties of secondary (repair) bonds on structural repairs must be greater than the original. This pretty much precludes the use of polyester on polyester as I don't think any experienced tech could argue that a secondary poly bond could be anywhere close to the primary.

ABS Specifically leaves the determination of materials and processes to the surveyor but does have an avenue for appeal. Here is the link to the appropriate USCG NVIC notice..

My ABS Rules for Construction of Plastic Reinforced Vessels is on my boat in Florida but if it becomes a bone of contention I could probably dig it out on line.
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Old 19-06-2017, 12:14   #40
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Re: Epoxy / Polyester Resins Question

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No standards organization will ever specify a specific product (resin) be used in any circumstance. What they do is lay out the requirements that product must meet.

ABS and the USCG requires that the adhesive properties of secondary (repair) bonds on structural repairs must be greater than the original. This pretty much precludes the use of polyester on polyester as I don't think any experienced tech could argue that a secondary poly bond could be anywhere close to the primary.

ABS Specifically leaves the determination of materials and processes to the surveyor but does have an avenue for appeal. Here is the link to the appropriate USCG NVIC notice..

My ABS Rules for Construction of Plastic Reinforced Vessels is on my boat in Florida but if it becomes a bone of contention I could probably dig it out on line.
Not to detract from this valuable contribution, but I think the requirement is effectively...the repair should be at least as strong as the original construction.

Using proper polyester FRP repair techniques, the repair is always as strong or stronger than original. This requirement does not preclude the use of polyester resin in any way.
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Old 19-06-2017, 12:20   #41
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Re: Epoxy / Polyester Resins Question

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Not to detract from this valuable contribution, but I think the requirement is effectively...the repair should be at least as strong as the original construction.

Using proper polyester FRP repair techniques, the repair is always as strong or stronger than original. This requirement does not preclude the use of polyester resin in any way.
As the investigating surveyor in an insurance claim I get to make that determination
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Old 19-06-2017, 13:17   #42
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Re: Epoxy / Polyester Resins Question

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IMHO best industry practice is , (and I have heard some insurance companies insist upon) repairs be made with like materials the vessel was originally constructed of.
Then you state: Not to detract from this valuable contribution, but I think the requirement is effectively...the repair should be at least as strong as the original construction.

You must see these two statements are contradictory - only one can be correct - so which is correct, IYHO? In your experience, do insurance cos insist on "the same material", or do they insist on "material being equally strong"?

A famous French builder of catamarans (I won't name them) had a bad batch of resin just a couple of years ago. All the repairs (all done under warranty) in this part of the world (entire South Pacific) were done by one boatyard, right here in NZ. Yes all South Pacific cats had to make their way here for repair, and yes (I'm sure you've guessed) the yard uses only epoxy, for all hull repairs.

They give a seven year guarantee on all repairs.
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Old 19-06-2017, 13:36   #43
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Re: Epoxy / Polyester Resins Question

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Most bedding materials have a life expectancy of about 10 years. This means that all wood core penetrations should be rebed (parts removed, core checked for wetness, dried or repaired if wet, and new bedding material applied to the joint, not just silicone sealant around the perimeter), every 10 years of the vessel life.
This is poor practice. Any penetration through a cored deck or hull must have the core material removed around the penetration and have the void filled permanently with epoxy to prevent moisture reaching the core (or have inner hull/deck modified so that it meets the outer surface without coring).
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Old 21-06-2017, 06:08   #44
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Re: Epoxy / Polyester Resins Question

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This is poor practice. Any penetration through a cored deck or hull must have the core material removed around the penetration and have the void filled permanently with epoxy to prevent moisture reaching the core (or have inner hull/deck modified so that it meets the outer surface without coring).
I whole-heartedly agree that resin potted core penetrations are superior, and I resin pot every penetration I make, as general practice.

This does not change the fact that the bedding compound should be replaced every 10 years as preventative maintenance.

While the resin potting will prevent core damage, it will not prevent the other damage as moisture enters the boat (chainplate bulkhead attachment points being a common one).

When I perform a deck core repair, I often offer the customer the options:

Good: Repair existing damage only.
Better: As above, remove, and rebed all other dry cored laminate fittings.
Best: As above but resin pot the penetrations.

Over 90% of the time, the customer will choose the Good option.

The other options are quite expensive to hire out, as it is very time consuming, and best done by two workers (at least for fitting removal and replacement), so the estimate is rarely approved.

The owner plans to do it themselves, and then rarely does (likely because he doesn't have a buddy or spouse that he can get excited to help him), and I receive another call down the road for deck repair in a new location, if they are not too embarrassed to admit the omission.
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Old 21-06-2017, 07:37   #45
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Re: Epoxy / Polyester Resins Question

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...When I perform a deck core repair, I often offer the customer the options:
Good: Repair existing damage only.
Better: As above, remove, and rebed all other dry cored laminate fittings.
Best: As above but resin pot the penetrations.
Over 90% of the time, the customer will choose the Good option...
Now I understand thanks, but:
- only modifications/core penetrations carried out by the owner should present core moisture problems, if the original builder was any good;
- only epoxy will work to seal these penetrations permanently.

The NZ yard I spoke of simply declines the work if 'Best' option is not taken - they let the owner do the job himself if he doesn't want it done properly - I guess that's the primary reason I bought this polyester (now epoxy sheathed - to waterline anyway) boat
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